Process of preparing detergent tablets



United States Patent 3,366,570 PROCESS OF PREPARING DETERGENT TABLETSArie Willem Slob, Schiedam, Netherlands, assignor to Lever BrothersCompany, New York, N.Y., a corporation of Maine No Drawing. Filed May14, 1962, Ser. No. 194,658 Claims priority, application Great Britain,May 15, 1961, 17,536/ 6 1 12 Claims. (Cl. 252-99) This invention relatesto detergent tablets and, in particular, to a method of preparingdetergent tablets from detergent powders.

It is an object of the invention to provide a detergent tablet which issufficiently hard for handling, packing and storing but which easilydissolves when added to water.

The invention provides a process for preparing a detergent tablet inwhich a detergent tablet containing a liquefiable substance and otheringredients, said liquefiable substance being capable of being liquefiedby heating without affecting said other ingredients, is agglomeratedinto the form of a tablet; the agglomerated detergent powder is heatedat a temperature and for a time sufii cient to convert at least part ofsaid liquefiable substance into liquid but insufiicient to affect saidother ingredients; and the agglomerated detergent powder is cooled toconvert said liquid into solid material, whereby said solid materialbinds the agglomerated detergent powder into a tablet.

The liquefiable substance referred to must be compatible with the otheringredients of the detergent powder and its liquefaction temperaturemust not be too high. Suitable substances include salts containing waterof crystallization such as sodium sulphate -hydrate, sodium carbonatel-hydrate, sodium perborate 4-hydrate, aluminum sulphate IS-hydrate,sodium borate IO-hydrate and alum 24-hydrates, especially potassiumaluminum sulphate 24-hydrate. The same salts with a lower hydratecontent may also be used. Salts such as anhydrous sodium carbonate andsodium hexametaphosphate which, it is believed, become at leastpartially hydrated when incorporated in a detergent powder by absorptionof water from the other ingredients of the powder and from theatmosphere may be suitable under certain conditions. Other substanceswhich may be used are sugar and gelatin.

Heating may be carried out in such a way that the agglomerated detergentpowder is uniformly heated or that only the surface of the agglomeratedpowder is heated. In the first case heating may be conveniently carriedout in microwave furnaces or by means of capacitive heating apparatus;in the second case heating may be carried out by contact heating, thatis, the surface of the agglomerated detergent powder may be heated bycontact for a short time with hot plates or hot air. Contact heatinggives particularly good results when hydrated sodium perborate is usedas the liquefiable substance. Contact heating may be carried out so thatthe tablet formed has a hard smooth crust, and a core of powder. Thecrust sufiiciently protects the powder contained in the interior of thetablet while the tablet is being handled. When such a tablet is put intowater it generally dissolves very quickly. The water penetrates into thesmall pores on the hardened surface layer, rapidly disintegrating thislayer and freeing the powder contained in the interior of the tablet.Alternatively, the process may be carried out in such a way that thewhole tablet is hard. Itis necessary that the liquefiable substance bedistributed homogeneously throughout the detergent powder.

3,366,570 Patented Jan. 30, 1968 The heating process of the inventionmay be compared to a sintering process, for the heating process must besuch that the detergent powder is not completely melted.

The temperature to be used during the process of the invention dependson the liquefiable substance which is used, the composition of thedetergent powder and the desired qualities of the product. If hydratedsodium perborate, which is the preferred material, is used thetemperature used is preferably between 60 and C. if all the agglomeratedpowder is heated, in order to restrict the decomposition of theperborate, but if only the surface of the agglomerated powder is heated,much higher temperatures may be used. When heat is applied only to thesurface of the agglomerated powder, the heat conductivity of thematerial is of importance. If the heat penetrates only slowly into thepowder it is in general possible to use temperatures of up to 300 C. Inother modifications of the invention temperatures as low as 40 C. may beused depending on the type of composition.

The amount of the liquefiable substance to be used also depends on theproperties of the substance itself and the detergent powder. The minimumamount of the liquefiable substance must be such that a satisfactorysintering action is obtained. The minimum amount of liquefiablesubstance is about 2% by weight of the powder; the upper limit isdetermined by the properties of the product which are desired.Percentages as high as 40% of liquefiable substance by weight ofdetergent powder may be used.

After the agglomerated detergent powder has been heated, the agglomeratemust be left for a certain time to cool before a satisfactory tabletresults. This resting time may be very much shortened by irradiating theproduct or placing it in a stream of air or under vacuum. In the lastcase, resting times of a few minutes are sufficient to obtain a verygood hard product.

The tablet may be further improved by a coating with a suitablesubstance. As g; sulastgpc gjhere maybe used, for example, xinyljfilfglf iggl ng; water glass. A

Further improvements may be obtained by treating the tablet for a shorttime with steam. In that way surface irregularities are removed and thesurface made smooth. The same effect may be obtained by sprinkling thesurface with water.

Very slight pressure is needed to bring the detergent powder into theenecessary agglomerated form for heat treatment; if it is desired tomake a very compact tablet, the pressure employed in this operation maybe slightly increased but it is a feature of the invention that tabletsmay be obtained without the use of high pressure compacting.

The following examples illustrate the invention:

Example 1 A high sudsing heavy duty detergent powder base of thefollowing composition was made:

Fluorescent brightening agent, perfume and preservative Water 10 11parts by weight of sodium perborate tetrahydrate were homogeneouslymixed with this detergent powder base. The resulting detergent powderwas placed in a per- The tablets obtained had very good properties, werere- I sistant to handling and were radially soluble in water.

The metal container may also be heated by means of high-frequencyinductive heating (eddy-currents and/or hysteresis losses).

If no perborate was added to the detergent no satisfactory tablet wasobtained.

Example 2 A controlled sudsing heavy duty detergent powder base of thefollowing composition was made:

12 parts by weight of sodium perborate tetrahydrate were homogeneouslymixed with this detergent powder base. An amount of the resultingdetergent powder suflieient to produce a tablet of dimensions of 69 x 57x 25 mm. was heated in a microwave oven with microwaves of 2450 me. Theheating by this method was homogeneous, that is to say, the energyabsorption of each part of the tablet was the same. The temperature ofthe powder rose above 120 C. within a few minutes. The perboratedecomposition, which is dependent on the amount of energy supplied, wasestimated at 10-15%. The tablets produced were very strong and could bedropped several times without breaking. They were readily soluble inwater.

Tablets were also produced by homogeneously sintering the powdertogether by means of capacitive heating. The agglomerated detergentpowder was brought between two condenser plates, to which an alternatingvoltage of 30 me. was applied. The tablets obtained were readilysoluble, but somewhat brittle.

Tablets were made of similar detergent powders in which the sodiumperborate was replaced by an equal amount of powdered sugar, sodiumcarbonate 10-hydrate, potassium aluminum sulphate 24-hydrate andaluminum sulphate 18-hydrate. Tablets with the same good properties wereobtained.

Tablets prepared without the addition of the above-mentioned componentswere very soft and rapidly fell to pieces.

Example 3 To each of a number of the units of agglomerated detergentpowder described in Example 2, 1.2 kcal. heat was transferred in 90seconds by means of inhomogeneous heating. Subsequently thedisintegration time under practical conditions of the tablets obtainedwas measured. This was done by moving the tablets constantly up and downin a basket in a certain amount of water at a constant temperature. Thedisintegration time of tablets obtained by using inhomogeneous heatingmethods with a heat transfer of 1.2 kcal. per 90 seconds, varied between30 and 15 seconds. The disintegration time of tablets obtained by usingmore heat, namely, 3.5 kcal. in 8.5 min., on average was 45 seconds.

4 Example 4 A controlled sudsing heavy duty detergent powder base of thefollowing composition was made:

Parts by weight Sodium alkylbenzene sulphonate 6 1 Soap 4 Sodiumsilicate 8 Sodium sulphate 15 t Nonionic 5 10 Sodium tripolyphosphate 42l Sodium carboxymethylcellulose 0.5 Fluorescent brightening agent,perfume and preservai tive 0.5 Water 9 In preparing the detergentcomposition the first four ingredients were spray-dried and mixed withthe other ingredients.

10 parts by weight of sodium perborate tetrahydrate were thoroughlymixed with this detergent powder base. An amount of the resultingdetergent powder was just sufiiciently pressed to obtain an agglomeratesuitable for the sintering operation. Such an agglomerate has no impactresistance. The tablet was brought into an electrically heated oven andheated for about 2 to 3 minutes with hot air, the temperature in theoven ranging from 240 to 275 C. In view of the low heat-conductivity ofthe powder the heating is inhomogeneous. The temperature inside thetablet reached values up to 65 C.

After cooling a tablet was obtained which could be dropped more than tentimes before breaking and which dissolved in water in about 75 seconds.The tablet was totally hardened.

Example 5 A controlled sudsing heavy duty detergent powder base of thefollowing composition was made:

Parts by weight i Sodium alkylbenzene sulphonate 4 1 Soap 6 49 Sodiumsilicate 8 Sodium sulphate l4 Nonionic 3 Sodium tripolyphosphate 27Sodium pyrophosphate 18 Sodium carboxymethylcellulose 1 Fluorescentbrightening agent, perfume and preservative 0.5 Water 10 The first fouringredients were spray-dried and mixed 50 with the other ingredients.

8.5 parts by weight of sodium perborate tetrahydrate were thoroughlymixed with the detergent powder base. An amount of the resultingdetergent powder was brought into tablet form by means of weak pressure.The agglo crate thus obtained had no impact resistance.

. The agglomerate was heated in an oven by means of circulating hot airto a temperature of about 190 C. for 6 minutes. The temperature in thecentre of the tablet was about 65 C. After cooling the tablet thusobtained could be dropped more than twenty times before breaking. Itdissolved in water in less than seconds. The tablet was totallyhardened.

Example 6 To a controlled sudsing heavy duty detergent powder base ofthe composition given in Example 2, 10% by weight of sodium perboratetetrahydrate was added. After thorough mixing a quantity of thedetergent powder was heated in a perforated metal box having dimensionsof 10 x 22 x 27 mm. by flame. A strong tablet was obtained, whichreadily disintegrated in water. The decomposition of perborate, however,was relatively high and more than 20% of the perborate originallypresent in the superficial layer was decomposed. A quantity of the samedetergent powder W45 heated in a metal mould of dimensions 50 x 50 x 30mm., placed in a transformer coil, as described in Example 1. In thisway the heating conditions could be better controlled, which resulted ina reduced decomposition of the perborate. With a heat transfer of 1.2kcal. in 90 seconds to the powder mixture, only about 15% of theperborate originally present in the superficial layer of about 1.5 mm.was decomposed. The mean perborate content was reduced from 10.2 to9.1%. The temperature reached at the centre of the tablet was about 50C. The same type of inhomogeneous heating may be effected by heating themould in an oven or by means of induction coils. The same results couldbe obtained without the use of moulds, by means of slightly prepressingthe powder into the form of a tablet and then applying the heatingmethod described above. Two kinds of tablets were produced, the onebeing hard on the outside and brittle inside and the other having a veryhard surface under which there was a somewhat brittle layer, theremainder consisting of loose powder. Both tablets had very goodproperties, being resistant to handling and readily soluble in water.

The resting time of the tablets made according to the foregoing examplescan be reduced to a few minutes by cooling the tablets after the heatingstep under vacuum. The surface of the tablets can be made smooth byadditional surface treatments, e.g. by treating the surface with steam,or hot water. The appearance of the tablets can be further improved bycoating the surface with polyvinyl alcohol, paraffin wax or water glass.A surface treatment with steam or hot water did not increase thedisintegration time of the tablets. Coating the tablets with waterglass, however, resulted in a slight increase of the disintegrationtime. Tablets with a disintegration time of 15-30 seconds had, aftercoating with water glass, a disintegration time of about 50 seconds.

What is claimed is:

1. A process for the preparation of a strong, hard surface, rapidlydisintegrating and dissolving detergent tablet which comprisesthoroughly mixing together a powdered detergent composition and fromabout 2% to about 40% by weight of the powdered detergent composition ofa liquefiable substance selected from the group consisting of hydratedsodium sulfate, hydrated sodium carbonate, hydrated sodium perborate,hydrated aluminum sulfate, hydrated sodium borate, hydrated potassiumaluminum sulfate, anhydrous sodium carbonate, anhydrous sodiumhexametaphosphate, sugar and gelatin having a liquefication temperaturefrom about 40 C. to about 300 C. and being compatible with theingredients in the powdered detergent composition, forming the resultingmixture having the compatible liquefiable substance uniformlydistributed therethrough into the shape of a tablet, heating thetablet-shaped mixture at a temperature from about 40 C. to about 300 C.for from about 90 seconds to about 6 minutes to liquefy thereby at leastthe portion of the liquefiable substance at the surface of thetablet-shaped mixture without completely melting the powdered detergentcomposition, and cooling the tablet-shaped mixture to convert theliquefied liquefiable substance to solid state and thereby bind togetherat least the portion of the powdered detergent composition at thesurface of the tablet-shaped mixture, whereby there is formed a strongdetergent tablet which disintegrates and dissolves in water in about 15to 75 seconds and which has a hard agglomerated surface portion and acenter portion having a consistency in the range from hard agglomeratesto loose powder.

2. The process as set forth in claim 1 wherein the forming of saidmixture into the shape of a tablet is performed by placing the mixtureinto a tablet-shaped mold.

3. The proces as set forth in claim 1 wherein the forming of saidmixture into the shape of a tablet is performed by lightly compressingthe mixture to tablet shape.

4. The process as set forth in claim 1 wherein the tablet-shaped mixtureis uniformly heated therethrough during the heating step.

5. A detergent tablet prepared by the process of claim 4 which compriseshard agglomerates throughout.

6. The process as set forth in claim 1 wherein only the surface portionof the tablet-shaped mixture is heated during the heating step.

7. A detergent tablet prepared by the process of claim 6 which comprisesa hard agglomerated surface portion and a center portion of loosepowder.

8. The process as set forth in claim 1 wherein the cooling of thetablet-shaped mixture is performed by placing it in a stream of air.

9. The process as set forth in claim 1 wherein the cooling of thetablet-shaped mixture is performed by placing it under vaccuum.

10. The process as set forth in claim 1 which comprises the further stepof coating the cooled detergent tablet with a material selected from thegroup consisting of polyvinyl alcohol, paraffin wax and water glass.

11. The process as set forth in claim 1 which comprises the further stepof treating the surface of the cooled detergent tablet with moisture tosmoothen the surface of the tablet.

12. The process as set forth in claim 1 wherein the liquefiablesubstance is a hydrated sodium perborate.

References Cited UNITED STATES PATENTS 1,457,217 5/1923 Dostal 252-922,444,837 7/1948 MacMahon 252-l35 2,807,559 9/1957 Steiner 16782.72,875,155 2/1959 Miles 252-138 2,876,200 3/1959 Strain et a1. 252-993,120,378 2/1964 Lee et a1 25299 X FOREIGN PATENTS 510,555 3/1955Canada.

OTHER REFERENCES Merrill, Industrial Applications of the SodiumSilicates February 1949, Industrial and Engineering Chemistry, p. 341.

LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, ALBERT T. MEYERS,

1. A PROCESS FOR THE PREPARATION OF A STRONG, HARD SURFACE, RAPIDLY DISINTEGRATING AND DISSOLVING DETERGENT TABLET WHICH COMPRISES THOROUGLY MIXING TOGETHER A POWDERED DETERGENT COMPOSITION AND FROM ABOUT 2% TO ABOUT 40% BY WEIGHT OF THE POWDERED DETERGENT COMPOSITION OF A LIQUEFIABLE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF HYDRATED SODIUM SULFATE, HYDRATED SODIUM CARBONATE, HYDRATED SODIUM PERBORATE, HYDRATED ALUMINUM SULFATE, HYDRATED SODIUM BORATE, HYDRATED POTASSIUM ALUMINUM SULFATE, ANHYDROUS SODIUM CARBONATE, ANHYDROUS SODIUM HEXAMETAPHOSPHATE, SUGAR AND GELATIN HAVING A LIQUEFICATION TEMPERATURE FROM ABOUT 40*C. TO ABOUT 300*C. AND BEING COMPATIBLE WITH THE INGREDIENTS IN THE POWDERED DETERGENT COMPOSITION, FORMING THE RESULTING MIXTURE HAVING THE COMPATIBLE LIQUEFIABLE SUBSTANCE UNIFORMLY DISTRIBUTED THERETHROUGH INTO THE SHAPE OF A TABLET, HEATING THE TABLET-SHAPED MIXTURE AT A TEMPERATURE FROM ABOUT 40*C. TO ABOUT 300*C. FOR FROM ABOUT 90 SECONDS TO ABOUT 6 MINUTES TO LIQUEFY THEREBY AT LEAST THE PORTION OF THE LIQUEFIABLE SUBSTANCE AT THE SURFACE OF THE TABLET-SHAPED MIXTURE WITHOUT COMPLETELY MELTING THE POWDERED DETERGENT COMPOSITION, AND COOLING THE TABLET-SHAPED MIXTURE TO CONVERT THE LIQUEFIED LIQUEFIABLE SUBSTANCE TO SOLID STATE AND THEREBY BIND TOGETHER AT LEAST THE PORTION OF THE POWDERED DETERGENT COMPOSITION AT THE SURFACE OF THE TABLET-SHAPED MIXTURE, WHEREBY THERE IS FORMED A STRONG DETERGENT TABLET WHICH DISINTEGRATES AND DISSOLVES IN WATER IN ABOUT 15 TO 75 SECONDS AND WHICH HAS A HARD AGGLOMERATED SURFACE PORTION AND A CENTER PORTION HAVING A CONSISTENCY IN THE RANGE FROM HARD AGGLOMERATES TO LOOSE POWDER. 